ACT: FLIRT?
by Darkhymns
Summary: Undyne and Sans don't always get along. Then Sans lays on the charm and that's when things take a disastrous turn. [Rated for mild language]
**Co-written with Sky's Penname. Guess which part he wrote..**

* * *

The one thing Undyne hated about Sans was how much of a lazyass he was.

Papyrus, by contrast, was a hard-working guy. Always ready to go past his limit, always understanding of just how important the power of friendship was, and always volunteering to do the next impossible task. That skeleton had big dreams and worked for it! Sans, she figured, just dreamed whenever she caught him snoring at his station. But she barely gave him a second thought when she was hanging out with her bestie Papyrus at their house in Snowdin.

"I'LL BE RIGHT BACK, UNDYNE! I WANNA SHOW YOU MY NEW SPAGHETTI INVENTION!" Papyrus was practically jumping up and down as he spoke to his best friend. "SPAGHETTI NICE CREAM! IT'S SO AMAZING!"

"Do you mean spaghetti-flavored nice cream?" she asked him carefully.

"NO. SPAGHETTI NICE CREAM. GLAZED WITH MINT AND THOSE LITTLE CHOCOLATE CHIPS AND EVERYTHING!" Papyrus had headed for the front door, limbs flailing. "I LEFT IT OUTSIDE FOR IT TO COOL NICELY. JUST WAIT RIGHT HERE."

"Hey! Let me come along-"

"NO!" Papyrus turned to her with shiny puppy-dog eyes, which was really quite impressive for someone with no eyes to speak of. "I – I WANT IT TO BE A SURPRISE."

She didn't have the heart to tell him that the surprise part was kind of ruined by now, but she played along. "Okay, fine, I'll wait. Just hurry up! I get bored easily!"

"I WON'T BE LONG. YOU AND SANS CAN HAVE FUN WHILE I'M AWAY." And then he had rushed off, cackling happily in the distance.

So Undyne was left standing in the living room of the skeleton brothers' house, with Sans perched on the couch. She hadn't even noticed him in the room for a good five minutes until she almost sat right on him.

"heya, fish face," said the skeleton with the grin carved onto his face.

"Hey." She glared with some disdain. "Shouldn't you be working?"

Sans shrugged. "on break, boss."

"You were on break when I saw you outside an hour ago!"

"yeah, but this is my _lunch_ break."

Undyne's eye twitched. "You're not even eating anything."

"on a diet." He laid back, eye sockets closed.

 _Annoying little punk._ "Seriously. If it weren't for Papyrus, I'd have sacked you ages ago!"

"i know." He opened one eye to look at her. "i really appreciate it."

"I'm not kidding, ya know!" She dropped heavily onto the couch, stretching her legs out, plopping her boots on the coffee table rudely. Any other normal person would've jumped at the very sound, though of course Sans wasn't close to normal. "Even when Papyrus complains about you, I can tell he's still being too soft! A skell like you needs to learn some discipline! So that you can actually do something for once!"

Shrug. "i'm good. 'sides, i think what me and paps have is working pretty well. not like he complains that much."

"Yeah, of course you'd think that, huh?" She linked her arms behind her head. "I try my best to give him the best training a friend like me can offer, but it sure doesn't help when he's got someone like you dragging him down."

Strangely, he didn't respond back as quickly as she thought he would. She turned, figuring he must have been napping, except he was looking at her, expressionless.

"…What?"

"that's pretty arrogant of you, ain't it?"

He spoke in a tone she definitely didn't like. Whatever. She was done with this conversation. "Gahh, shaddup, you're being lame!"

"alright."

So she waited, sitting on the couch, with Sans next to her, the silence building up between them. She gnawed on her lip impatiently, a daring feat considering her fangs were razor-sharp and could cut clean through metal if she wasn't careful. (Her bitten off kitchen utensils were proof of this). She strained her ears to listen for a familiar 'nyeh,' but none came.

" _This is so boring!"_ She yelled, tugging at her hair. She turned furiously on Sans, half-convinced this was all his fault. "How the heck do you stand it?"

Sans shrugged in reply. Who the hell just shrugs like that?

"maybe you should try reading," he said to her after a moment.

Undyne scoffed at the suggestion. "Reading's for wimps!" She reconsidered. "Unless you got those human history books with the swords and princesses!

"sorry, fresh out." There was suddenly a large thick book in his hand. She had already gotten used to Sans' dumb parlor tricks by now.

"What's that?"

"a book."

"What kind of book?"

"my book."

Snatching it away from him, she gripped it between her hands as if she would rip it in half (which was very likely.) On the cover, it said, _Top Jokes to Win Gals._

"Dude, is this some kind of pick-up book?" she asked, laughing.

Sans shrugged _again._ But at least he answered her with actual words fairly quickly. "yeah, I pick up books all the time."

Ignoring that, she opened it up, and was surprised to find another book inside, the title along the lines of 'something something quantum mechanics.' She opened that one, and found another quantum mechanics book. Then she opened that one, and found another-

She threw the book(s) in the air, roaring furiously. "What kind of stupid crap is this?"

"i'm just really into science fiction."

"You are such a nerd!"

"yeah," he admitted. And then the weird thing – he turned to her, and gave her a wink. His constant smile was wide. "but you like nerds, don't ya?"

Uh.

What.

Undyne actually couldn't think up much of a comeback at first, until she felt her lungs bubble up with more laughter. Nervous laughter, but maybe he couldn't tell the difference? "The heck? Haha! I only like tough people! No nerds allowed!" Well, except one nerd. But come on, no way he actually knew about that? He was just being a cocky little jerk like always. "I'm not the one with a _dumb joke book!"_

"chicks love a funny guy." Sans was leaning his skull into his palm, elbow perched on his knee so casually as he looked at her. "see, you're laughing."

"I'm not! I'm – I'm just choking on saliva!" She proceeded to cough, because for a moment, she actually was choking on her saliva, swallowing too much air as she did so. That happened occasionally. "Don't be so full of yourself!"

"as a skeleton, i'm not really full of anything."

 _Oh my god._ "Can you go back to being quiet?"

"sure, just uh, heads up."

She blinked, then raised her working eye to the ceiling. In the back of her mind, she had wondered why the book she had thrown hadn't actually come down yet. The moment she upturned her head, the book landed squarely on her face, making a big 'thud' sound.

Growling, she reached up, intending to not only shred the book, but eat it for breakfast, when she caught sight of the title. Mostly the same, except…

 _Top Jokes to Win Fish Gals,_ the 'Fish' part having been added in permanent marker.

That was when she turned, and found Sans standing right next to her on the couch, his skull really, really, _really_ close.

"hey," he said, his voice low, like a whisper. She could practically feel his breath on her ear and- wait, was that a finger trailing just underneath her chin all soft-like and what the fuck what the fuck. "wanna have a good time?"

So Undyne did what any sane person would do.

She immediately kicked him in the face.

" _NGGAAAAHH!"_ Her battle roar could shatter glass, which it did. The winter breeze blew in through the now very drafty windows, already bringing in snow. A glowing spear was in her hands. _"The fuck is wrong with you?!"_

She looked around, thinking she would see Sans completely submerged in the wall of the house because of her incredible kick of pain. But instead he was nowhere. Actually, had she felt anything when she kicked him? It had felt more like she had been hitting air, but she figured it was because the skeleton was just some dumb shorty that was full of hot air. That was when she felt a tapping on her shoulder a second later.

"pretty rude of you, undy."

She whirled around, slashing with her spear. Sans sidestepped away, perched on the top edge of the couch. His usual grin had an air of smugness. "taking some advice from tsunderplane, i see."

"If you're trying to mess with me, it's not gonna work!" She waved her arm, and spears flew through the air in an arc. One hit the television set, another hit the table with the pet rock (said rock was just fine), and another pinned itself against the ceiling. Sans dodged every one with half-steps, hands in his pockets.

"aww." He was grinning way too much. "don't be so _koi."_

Angry fish noises gurgled out of her throat. She forgone her spears to do a good ol' fashioned tackle. Sans vanished when she was just inches away, making her crash into the floor, face-first.

"always knew there was something fishy going on between us."

Undyne got up, and then decided to lift up the couch over her head. Because she could! "That doesn't even make sense!"

Sans' right eye socket twitched. "look, i'm trying my best here. god damn."

"You should try your best at _being dead!"_

"nah."

She charged again at the skeleton, hurling the couch at him as she did so. Another instance of his disappearing act, and the couch had crashed into the wall, followed by an explosion of plaster and couch stuffing but not, unfortunately, the bones of an annoying prankster.

"You crossed the line with that stupid crap!" she shrieked at him.

"hey, just jokes between best pals." Then he narrowed his eye sockets, hunching his shoulders a little bit. "that's what we've been doing the entire time, right? just good ol' jokes about ourselves and uh, our character."

Undyne wasn't dense. She heard that edge in his voice. Well, maybe the guy wasn't such a lazyass after all! "If you're angry with me, then you should just say it and fight me like a true warrior!" She pounded a scaly fist against her chest, her grin sharp, and slightly bloodthirsty. "Come on, give me your best shot!"

Sans waved her off. "eh, not my style. i'd rather just mess with ya until ya tire yourself out."

Undyne had never felt more offended then in this very moment. "That is such a wimpy-ass move that I think I'm gonna hurl just thinking about it."

"rather you didn't. this place already smells like sushi."

"NGAAAHHH!" Undyne summoned a spear that was three times her height and launched it again at the skeleton. The motion had taken much out of her, bringing her to her knees. Her attack had been huge. No way she could have missed!

A quick jump and again she missed, and then Sans was standing right next to her, his head even with hers now that she was down. He laid a flimsy hand on her shoulder, leaning in close with that grin of his.

"sorry, babe. guess my flirting skills are too much for ya to handle-"

"WHAT?" Undyne stood up, clenched her fists, then turned to glare down at the puny skeleton with all her might. A grin creeped up her face yet again. "You think I can't match up against your flirting power?!"

The skeleton was not at all deterred, and showed that with another wink. "no, but hey, maybe that's a good thing. after all, opposites attract, right?"

She didn't lash out in anger this time. Instead, she grinned back even harder. "You're not gonna make me give up that easily."

Sans was usually a pretty good dodger, and he would've easily evaded her next attack had a ring of spears not just surrounded him then. They were filled with a green light, so bright it actually made Sans blink more than once. Magic countered against his own for a quick second, but that was enough, because green magic was a tricky magic, second only to blue.

Sans felt his limbs lock into place. "uh."

Undyne marched up to him in less than two strides. "When you're green, you can't escape!" She pointed at him with an accusing finger. "Unless you learn to face danger head-on!"

Instead of swiping at him with another spear like he expected, the fish warrior grabbed him by the midriff, carried him through the air, and then slammed him against the wall of spears. She leaned into him, one hand on his bony waist, the other gripping the front collar of his shirt with an almost desperate twist.

Strands of her now red hair fell over her face. Her sole eye shone with determination, and her grin was practically a leer by this point.

"Fuhuhuhu. By the time I'm through with you, _you're gonna be head over heels for me."_

Sans shifted his eyes around at his very precarious position. "uh, i might, if you're not careful." He edged one gaze at the hand that was juuust right above his shorts. "hey, don't the rules say we need to have dinner first before we go to third base-"

" _Rules are meant to be broken!"_

A door creaked as Papyrus strolled into the living room, his creation a glopping mess in his hands. He felt completely satisfied with it and was feeling particularly excited to show it to his friend/bro. "GUYS I'VE GOT A GREAT TREAT FOR BOTH OF YOU-"

Undyne turned, momentarily distracted. It was enough for Sans to blip out of her hold a good distance away from the green magic aura. The skeleton turned to a confused Papyrus with a thumbs up. "thanks for the save, bro."

The fish warrior growled. "I challenge you to a fight to the death!" Undyne howled. Her boot crushed the coffee table into hundreds of pieces, fully completing the destruction of all items in the living room.

Sans shrugged. "yea, sure, cool."

The spaghetti nice cream plopped onto the carpet. "AW, NOT THE LAVA PIT I HOPE…"

* * *

Scorching steam blew through the air as red hot lava bubbled beneath them. A long rather thin wooden board was the only thing separating the two from a rather unpleasant demise. The stony cave walls glowed an intimidating red, reflecting the dangerous liquid of Hotland below.

"Exactly the lava pit!" Undyne shouted, spear gripped above her head and all the while laughing uncontrollably like a maniac.

Papyrus frowned but kept a steady hand on his bowl of now melted-ice-cream-spaghetti. "WELL, TRY NOT TO KILL EACH OTHER THAT MUCH. I STILL WOULD REALLY LIKE YOU GUYS TO TRY MY SURPRISE!" he shouted from the edge of a cliff in a much safer position.

Hands still deep in his coat pockets, Sans showed no signs of the heat affecting him. The board was just wide enough for him to keep a relaxed stance. "you don't have to worry about me, bro. i'm gonna keep my _cool_ even if things have _heated_ up."

"ON SECOND THOUGHT, PLEASE KILL HIM, UNDYNE."

Hot air blasted through Undyne's hair, whipping it heroically in all directions. Her fangs shone in a wild grin. "Oh, I'll enjoy it too! You ready, you little punk?" She stamped a scaly foot on the board, causing it to shift and shake dangerously for the both of them. She had forgone her usual armor for her casual outfit to better suit the temperature and give Sans the fighting chance he needed.

Sans scratched an itch on his behind, the vibrations of the platform seeming to completely pass around him. "oh, i was _bone_ ready." He winked. Papyrus audibly scowled.

No more wasting time! Undyne barreled down the board towards her enemy, her stance perfectly balanced. As adrenaline pumped through her veins, crazy laughter escaped her lips.

"wow, didn't think i was _that_ funny," Sans chuckled, staying put on his end, hands still tucked away in his pockets.

"NGGGGGAAH!" Undyne stabbed and slashed after her opponent. The wind whistled with each strike, leaving an afterimage of green light that was blinding to the eyes. Yet each attack seemed to barely miss. Sans didn't appear to even be moving, but Undyne couldn't hit him? "Stay still, you little shit!"

"i am," he grinned, no more than usual, yet it seemed to insult Undyne's pride.

Eye wide in fury, she thrusted her spear forward, fully intending now to break the skeleton's brittle skull. This time she didn't miss. Instead, her spear crashed into nothing but air. Sans was gone completely.

 _Pfffffffbt._ A whoopee cushion blew into her left ear from behind. Undyne squealed in shock and lost her balance, arms waving and pumping with little control. A foot scraped the edge of the board, and soon her entire body falling with it.

The bubbling sea of molten rock and hissing steam was quickly catching up to her in her descent. Her hands reached for a hold, but couldn't grab anything in time. It was too late to save herself now.

The world became a spinning heated mess as the warrior met her fate. Just as she seemed to accept that her life was over, the spinning stopped. A bony hand grasped hers tight as she dangled above certain death.

"Sans?" she breathed out in disbelief. "You saved me?"

Undyne looked up at that grin again, but this time didn't see that smug smile. Instead, it seemed almost caring and warm. Not just because the lava or anything. "of course. i'm not about to let my friend turn into fish soup."

Her eye went wide, and Undyne's raging heart finally soothed. "Sans… you really… you really are…" she grabbed the board with her free hand and pulled down _hard_ with the other, throwing the skeleton off the wooden platform. "A gullible nerd!" she cackled.

"what." The skeleton was genuinely surprised. His arms were already completely out of range of anything to grab ahold of now. Sans' eye sockets finally emoted a pure and real shock. Meanwhile, Undyne merely waved a sarcastic goodbye.

" _HOOOOOOOOOOOOOO YEAAAAAAAAAAAH!"_ Undyne cheered as she returned to the cliff side to greet Papyrus. "I won, I won, I WON, YEAH. Who's dunking who now!?" She flicked a spear to twirl in her hand.

Sans appeared in front of her, sweat dripping from his skull. "you seriously attempted to kill me after i saved your life. i had zero intentions of ever actually hurting you."

Papyrus was hooting and hollering with Undyne. She gulped down a bowl of victory ice cream spaghetti, which was completely mush at this point. The taller skeleton patted his brother on the back. "DON'T BE SUCH A SORE LOSER, SANS! SHE BEAT YOU FAIR AND SQUARE!"

"i would have actually died."

"IT _WAS_ A BATTLE TO THE DEATH, BRO."

"are you both serious right now?"

But they were too busy high-fiving each other, laughing together in glee. "THIS IS WHY WE ARE FRIENDS, UNDYNE!" Papyrus shouted happily.

"holy fuck."

* * *

"THAT WAS REALLY SUCH AN INTENSE BATTLE. IT IS QUITE DIFFERENT FROM THE CALM GATHERING WE'RE HAVING RIGHT NOW."

"Yeah, it's so lame in comparison."

Sans, seated at the kitchen table with both Papyrus and Undyne, didn't say anything. In fact, he hadn't said much of anything throughout the entire walk back home, or throughout the entire 'celebration dinner for the Undyne-Dunking-Sans' party. There were still a few open holes in the walls of the skeleton brother's home, some leftover spears lying around, and the couch was now broken in half, but the house itself was at least still standing, and that was what counted.

Undyne gave Sans a friendly punch on the shoulder, seeing his glum look. "Come on, punk! It ain't like ya to mope! I mean, you should've expected to get your ass beat when you challenged me!"

When Sans talked, it was with the same chill tone as before. "well, actually you challenged _me_. but you know, it's fine." He shrugged.

Undyne sipped down her ravioli milkshake, courtesy of Papyrus. She was still riding high on her previous triumph and wouldn't flinch away from the taste. "Yeah, yeah. So basically, we're even now, aren't we?"

"sure. you dunked me fair and square." A pause. "literally."

"Hey, how about I train you with Papyrus? If you get good enough, I bet you'll beat me one day!" She laughed uproariously, slamming an open hand against the already shattered table.

Papyrus, who was seated on the other broken half of the table, looked to his brother with excitement. "WOULDN'T THAT BE FUN, SANS? THEN YOU WON'T ALMOST DIE NEXT TIME."

No one noticed the faint twitch on Sans' cheekbones. Not even Sans, who brushed it all away with a smile. "think i'll pass, but hey, undyne." He held out a hand to her. "i forgot to congratulate ya. you know, for beating me and all."

She narrowed her good eye at him. "You can't fool me. You're just gonna get me with one of your stupid fart jokes."

"hey, don't worry." He showed her his empty hand, baring his skeletal fingers, and even pulled up the sleeve of his hoodie show off his bare arm bone. "see? nothing up my sleeve. heh."

Undyne, though not fully convinced, didn't want to back out. She wasn't a wimp! She latched her strong, scaly hand with his boney, weak one. "Thanks, punk! I guess you ain't so bad."

Sans kept his grin as they shook hands. "yeah, sure." Then he kept grinning, and suddenly she felt a slight pulling and he moved toward her hand like he was going to kiss it-?

Uh!

She flinched, slipping her hand away from him. Only then did she notice something was in her palm.

He had passed her a small, tiny valentine heart. She stared at it, puzzled.

 _call me for a good time,_ it said in sloppy writing.

Then a breathy whisper in her ear. "cuz i'm in the mood for hot fishcakes."

" _NNNGGAAAHHHH!"_ And with that powerful roar of fury, Undyne upended the already destroyed table, aiming it for Sans who had long teleported away to be next to his brother.

Papyrus gave a long-suffering sigh as his kitchen was wrecked. "SANS. THAT WAS VERY UNSPORTSMAN-LIKE OF YOU."

"yeah." Sans shrugged. "just not a very sporting guy, is all."

"Fight me again!"

"hey, didn't ya hear me?" And then Sans teleported much farther, though not far enough to not hear Undyne's battle-cry that rung throughout the entire Underground.


End file.
